I have a pretty similar machine as you (bh6, 1ghz, win98). I tried the 12.40's and got stable performance but low 2001 3dmarks. I uninstalled and tried 10.80's and got much better 3d performance. It didn't seem unstable, but I got a couple unexplained ramdom lockups in games that I attributed to buggy software/os or o/c'd video card and processor.